Optical sights or scopes are used for a variety of purposes, one of which is to help a person accurately aim a firearm such as a rifle or a target pistol. The optical sight is typically mounted on the barrel of the firearm, and the person uses the sight to view the intended target in association with a reticle, often with a degree of magnification. Some sights have a tumbler that can be moved between two different positions in order to change the degree of magnification. That is, when the tumbler is in one position, the user sees the intended target with one degree of magnification, and when the tumbler is in the other position, the person sees the same target with a different degree of magnification.
Still another approach is to omit the tumbler and provide a split field of view, where the person simultaneously sees the same target with different degrees of magnification. Although pre-existing optical sights with split fields have been generally adequate for their intended purposes, they have not been satisfactory in all respects.